1. Field of the Invention
The present invention relates to methods of inhibiting the corrosion of metal surfaces by aqueous acids and corrosion inhibiting compositions therefor.
2. Description of the Prior Art
Subterranean hydrocarbon containing formations penetrated by well bores are often treated with aqueous acids to stimulate the production of hydrocarbons therefrom. One such treatment generally referred to as “acidizing” involves the introduction of an aqueous acid solution into a subterranean formation under pressure so that the acid solution flows through the pore spaces of the formation. The acid reacts with acid soluble materials contained in the formation thereby increasing the size of the pore spaces and increasing the permeability of the formation. Another production stimulation treatment known as “fracture-acidizing” involves the formation of one or more fractures in the formation and the introduction of an aqueous acid solution into the fractures to etch the fracture faces whereby channels are formed therein when the fractures close. The acid also enlarges the pore spaces in the fracture faces and in the formation.
Acidizing and fracture-acidizing solutions typically contain, for example, 15% to 28% hydrochloric acid which causes corrosion of metal surfaces in pumps, tubular goods and equipment used to introduce the aqueous acid solutions into the subterranean formations to be treated. The expense associated with repairing or replacing corrosion damaged tubular goods and equipment can be very high. The corrosion of tubular goods and down-hole equipment is increased by the elevated temperatures encountered in deep formations, and the corrosion results in at least the partial neutralization of the acid before it reacts with acid-soluble materials in the formations.
Aqueous acid solutions are also utilized in a variety of other industrial applications to contact and react with acid soluble materials. In such applications, metal surfaces are necessarily also contacted with the acid and any corrosion of the metal surfaces is highly undesirable. In addition, other corrosive fluids such as aqueous alkaline solutions, heavy brines, petroleum streams containing acidic materials and the like are commonly transported through and corrode metal surfaces in tubular goods, pipelines and pumping equipment.
A variety of metal corrosion inhibiting additives have been developed for aqueous acid fluids; however, many of them are considered environmentally objectionable. Cinnamaldehyde which has favorable environmental characteristics has been used for years in corrosion inhibitor formulations; however, the cinnamaldehyde molecule by itself provides only limited inhibition in 15% hydrochloric acid at temperatures greater than 225° F. and in 28% hydrochloric acid at temperatures greater than 200° F. Since cinnamaldehyde is one of the more ecologically benign organic materials in acid corrosion inhibiting compositions, improvements in cinnamaldehyde-based chemistry are actively pursued.
Some improvements have been made to the corrosion inhibiting properties of cinnamaldehyde by combining it with quaternary aromatic amine salts along with acid soluble antimony or bismuth to achieve improved corrosion inhibition of high chromium steel. Other efforts have concentrated on high density brines to which an aldehyde, a primary amine and a thiocyanate salt are added.
There remains a continuing need for improved methods and metal corrosion inhibiting compositions which are effective when combined with aqueous acids, especially at elevated temperatures.